In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation such as g-line and i-line radiation has been used, but nowadays, mass production of semiconductor elements using KrF excimer lasers and ArF excimer lasers has already commenced. Investigations are also being conducted into the use of even shorter wavelength sources than the above excimer lasers, including F2 excimer lasers, electron beams, extreme ultraviolet radiation, and X-rays.
Furthermore, one example of a pattern-forming material capable of forming a pattern of minute dimensions is a chemically amplified resist, which includes a base material component with a film-forming capability, and an acid generator component that generates acid on exposure. Chemically amplified resists include negative compositions, which undergo a reduction in alkali solubility on exposure, and positive compositions, which display increased alkali solubility on exposure.
Conventionally, the most common base material components used within pattern-forming materials such as resists are polymers with a weight average molecular weight of at least 5,000.
In this description, the term “base material for pattern formation” refers to the main material responsible for forming a pattern structure.
However, when a pattern is formed using this type of pattern-forming material, a problem arises in that roughness can develop on the upper surface and side wall surfaces of the pattern.
This type of roughness has conventionally posed few problems. However in recent years, with the rapid miniaturization of semiconductor elements and the like, ever higher levels of resolution such as width dimensions of no more than 90 nm are being demanded, and this miniaturization has meant that roughness is becoming a more serious problem. For example, when a line pattern is formed, roughness on the side wall surfaces of the pattern known as LER (line edge roughness) causes fluctuation in the line width that is formed, and although the degree of this fluctuation in the line width is preferably suppressed to no more than approximately 10% of the width dimension, the effects of LER increase as the pattern dimensions are reduced. For example, when a line pattern with dimensions of approximately 90 nm is formed, the degree of the fluctuation in the line width is preferably suppressed to no more than approximately 10 nm.
However, the polymers typically used as base materials have a large root mean squared radius per molecule of several nm, meaning the degree of fluctuation described above is equivalent to the width of only a few polymer molecules. As a result, as long as polymers are used as the base material component, reductions in LER will remain extremely difficult to achieve.
On the other hand, the use of low molecular weight materials containing alkali-soluble groups such as hydroxyl groups, wherein either a portion of, or all of, the hydroxyl groups are protected with acid dissociable, dissolution inhibiting groups, as the base material has also been proposed (for example, see patent references 1 and 2). These low molecular weight materials have small root mean squared radius values as a result of their lower molecular weight, and as such, their contribution to LER is expected to be minimal.
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. 2002-099088
[Patent Reference 2]
Japanese Unexamined Patent Application, First Publication No. 2002-099089